
function objString(obj) {
    let str = '';
    for (var key in obj) {
        str += `${key}=${obj[key]}&`
    }
    return str.slice(0, str.length - 1);
}

// 封装Ajax函数
function ajax(method, url, params, cb) {
    let xhr = new XMLHttpRequest()
    xhr.open(method, method == 'get' ? url + "?" + objString(params) : url)
    xhr.obreadystatechage = function () {
        if (xhr.readyState == 4) {
            cb(JSON.parse(xhr.responseText))
        }
    }
    xhr.setRequestHeader('content-type', 'application/x-www-form-urlencoded');
    xhr.send(method == 'get' ? null : objString(params))
}